1. Field of the Invention
The invention relates to solid industrial rubber tires and to the manufacture thereof. More particularly, the invention relates to new methods and apparatus for manufacturing such tires using injection molding technology whereby unvulcanized rubber compound is injected into a mold cavity surrounding a steel band to which the rubber is bonded during vulcanizing to form a solid press-on industrial rubber tire. Further, the invention involves new mold constructions and molding procedures which permit vulcanizing the injected rubber compound and bonding thereof to a steel band in an extremely short period of time without steel band distortion from extremely high injection molding pressures required during injection, molding and vulcanizing, which results in finished products having very favorable characteristics.
2. Description of the Prior Art
The manufacture of solid industrial steel-banded rubber tires heretofore has been carried out using compression molding procedures, techniques and equipment. Such compression molding procedures usually have required a two- to three-hour cycle per tire for carrying out molding, vulcanizing and related operations to form a finished product.
These compression molding operations include individually applying to predetermined quantity of unvulcanized rubber compound to and around a steel band, inserting such rubber-compound-surrounded band into an open mold cavity, closing the mold, locating the mold under compression in various known types of heating equipment, and heating the mold to vulcanize the rubber and bond it to the steel band. A relatively large loss of rubber in the flash formed between mold components results in carrying out such compression molding operations. This rubber loss occurs because the predetermined amount of rubber compound applied to and around the steel band before mold cavity insertion must be sufficient to assure by overfill or overflow that the mold cavity is completely filled with rubber when closed and heated under pressure.
Compression molding procedures have been used for the manufacture of bushings consisting of inner and outer spaced metal sleeves or shells with an intervening annular rubber body vulcanized and bonded to and between the metal sleeves such as shown in Lord U.S. Pat. No. 2,187,165. These bushings are molded by axially pressing end caps toward each other to confine the rubber body under pressure during vulcanizing. The end caps engage the ends of the spaced sleeves and also impart compression forces during molding to unvulcanized rubber compound located between the sleeves. Excess rubber overflows from the rubber body between the sleeves into an overflow space. A thick-walled metal pressure tube surrounds a thin outer bushing sleeve during molding to prevent bulging of a thin sleeve from the pressure maintained on the rubber during vulcanization. Such compression molding procedure for the manufacture of such bushings involves many of the same disadvantages described above concerning the compression molding of solid industrial steel-banded rubber tires.
Some of these problems related to compression molding of bushings were sought to be solved by the injection molding of torsion springs or bushings set forth in the Krotz U.S. Pat. No. 2,724,864 wherein the inner and outer metal sleeves or bands have substantial radial thickness and are engaged at their ends by annular sealing projections carried by the upper and lower mold members which bite into the ends of the metal sleeves when the mold is closed to seal the joints thus formed against seepage of rubber compound injected into the space between the sleeves. The filled mold after injection is then transferred and held under pressure between heated plates of a vulcanizing or curing press. However, during injection and vulcanizing there is nothing in Krotz to prevent distortion of the inner sleeve from the pressure developed during injection of the unvulcanized rubber compound into the annular cavity between the inner and outer sleeves. Further, in the Krotz procedure, after the mold has been closed and injected, when it is transferred to the curing press there is nothing to maintain injection pressure on the injected rubber in the space between the sleeves during vulcanization. Thus the Krotz curing step is essentially a compression molding step.
Insofar as we are aware, there have been no solid industrial steel-banded rubber tires produced by complete injection molding procedures before the first production thereof in accordance with the invention. Thus, an injection molded steelbanded industrial rubber tire has been unknown in the art prior to our invention; and there has been a want existing in the art for procedures and equipment by which an injection molded steelbanded industrial rubber tire could be produced with the attendant advantages of injection molding including high quality finished products and short curing times.